The third National Health and Nutrition Examination Survey (NHANESIII) collected descriptive data, physical measures, and biomedical samples (blood and urine) on a representative U.S. sample of children at ages two months through six years with over sampling for Blacks and Mexican Americans. Serum cotinine levels were measured and information on prenatal maternal smoking obtained. NICHD supported acquisition of birth certificates from the States to link the extensive data from NHANESIII to the child's birth certificate to use the prenatal and birth information. Results of the linkage are being used in research efforts on the following: 1) to determine if low birth weight or premature children have subsequent poor health as measured by biomedical markers in a representative national sample of children through age six; 2) to assess the effects of ethnic/racial and socioeconomic factors on these outcomes; 3) to develop normative growth and other biomedical scales for a U.S. representative population, and Black and Mexican-American children, according to a risk profile at birth; and 4) to develop comparisons between maternal and proxy reports of children's risk factors at birth and actual measurements for use in other studies. The first findings include the following: 1) Significant effects of birth weight on growth persist through the first six years of age at p<0.001. The relative deficits for low birth weight (LBW) children and excesses for high birth weight (HBW) children are larger for linear measures (length and height) and measures of muscularity and lean body mass than measures of subcutaneous fatness. For length/height, upper arm and thigh muscle areas, LBW children were 0.5 standard deviations below the mean for normal (NBW) weight children through age six. HBW children were 0.4 standard deviations above the mean. 2) Exposure to environmental tobacco smoke (ETS) accounts for approximately 40-60% of respiratory morbidity in children ages 2 months to 5 years. ETS exposure increased the prevalence chronic bronchitis and wheezing among 2 months to 2 year olds and asthma across all ages. For household exposure, a consistent effect was seen only at 20+ cigarettes a day.